This verse points out the two classes for which the book will be useful:
(1) the "simple," literally the "open," the open-hearted, the minds ready to receive impressions for good or evil Proverbs 1:22; and
(2) the "young," who need both knowledge and discipline.
To these the teacher offers the "subtilty," which may turn to evil Exodus 21:14 and become as the wisdom of the serpent Genesis 3:1, but which also takes its place, as that wisdom does, among the highest moral gifts Matthew 10:16; the "knowledge" of good and evil; and the "discretion," or discernment, which sets a man on his guard, and keeps him from being duped by false advisers. The Septuagint renderings, πανουργία panourgia for "subtilty," αἴσθησις aisthēsis for "knowledge," ἔννοια ennoia for "discretion," are interesting as showing the endeavor to find exact parallels for the Hebrew in the terminology of Greek ethics.

To give subtilty to the simple - The word simple, from simplex, compounded of sine, without, and plica, a fold, properly signifies plain and honest, one that has no by-ends in view, who is what he appears to be; and is opposed to complex, from complico, to fold together, to make one rope or cord out of many strands; but because honesty and plaindealing are so rare in the world, and none but the truly religious man will practice them, farther than the fear of the law obliges him, hence simple has sunk into a state of progressive deterioration. At first, it signified, as above, without fold, unmixed, uncompounded: this was its radical meaning. Then, as applied to men, it signified innocent, harmless, without disguise; but, as such persons were rather an unfashionable sort of people, it sunk in its meaning to homely, homespun, mean, ordinary. And, as worldly men, who were seeking their portion in this life, and had little to do with religion, supposed that wisdom, wit, and understanding, were given to men that they might make the best of them in reference to the things of this life, the word sunk still lower in its meaning, and signified silly, foolish; and there, to the dishonor of our language and morals, it stands! I have taken those acceptations which I have marked in Italics out of the first dictionary that came to hand - Martin's; but if I had gone to Johnson, I might have added to Silly, not wise, not cunning. Simplicity, that meant at first, as Martin defines it, openness, plaindealing, downright honesty, is now degraded to weakness, silliness, foolishness. And these terms will continue thus degraded, till downright honesty and plaindealing get again into vogue. There are two Hebrew words generally supposed to come from the same root, which in our common version are rendered the simple, פתאים pethaim, and פתים or פתיים pethayim; the former comes from פתא patha, to be rash, hasty; the latter, from פתה pathah, to draw aside, seduce, entice. It is the first of these words which is used here, and may be applied to youth; the inconsiderate, the unwary, who, for want of knowledge and experience, act precipitately. Hence the Vulgate renders it parvulis, little ones, young children, or little children, as my old MS.; or very babes, as Coverdale. The Septuagint renders it ακακοις, those that are without evil; and the versions in general understand it of those who are young, giddy, and inexperienced.
To the young man - נער naar is frequently used to signify such as are in the state of adolescence, grown up boys, very well translated in my old MS. yunge fulwaxen; what we would now call the grown up lads. These, as being giddy and inexperienced, stand in especial need of lessons of wisdom and discretion. The Hebrew for discretion, מזמה mezimmah, is taken both in a good and bad sense, as זם zam, its root, signifies to devise or imagine; for the device may be either mischief, or the contrivance of some good purpose.

To give subtilty to the (e) simple, to the young man knowledge and discretion.
(e) To such as have no discretion to rule themselves.

To give subtlety to the simple,.... Men of mean abilities, weak capacities, shallow understandings, incautious, credulous, and easily imposed upon: these, by attending to what is herein contained, may arrive to a serpentine subtlety; though they are simple and harmless as doves, may become as wise as serpents; may attain to an exquisite knowledge of divine things and know even more than the wise and sage philosophers among the Gentiles, or any of the Rabbins and masters of Israel; or any of the princes of this world, whose wisdom comes to nought; and become very cautious and circumspect how they are drawn aside by the old serpent the devil, or by such who lie in wait to deceive; and perform their duty both to God and man;
to the young man knowledge and discretion; or "thought" (i); who wants both: this book will teach him the knowledge of things moral, civil, and religious: to think and act aright; how to behave and conduct himself wisely and discreetly before men; and be a means of forming his mind betimes for piety and religion; and of furnishing him with rules for his deportment in future life, in all the periods of it; and in whatsoever state and condition he may come into. A "young man may cleanse his way", Psalm 119:9, reform his manners, behave with purity and uprightness, by taking "heed" to the things herein contained.
(i) "cogitationem", Pagninus, Mercerus; "bonam cogitationem", Michaelis.

simple--one easily led to good or evil; so the parallel.
young man--one inexperienced.
subtilty--or prudence (Proverbs 3:21; Proverbs 5:21).
discretion--literally, "device," both qualities, either good or bad, according to their use. Here good, as they imply wariness by which to escape evil and find good.

This verse presents another aspect of the object to be served by this book: it seeks to impart prudence to the simple. The form פּתאים
(Note: Like עפאים, Psalm 104:12, וכצבאים, 1-Chronicles 12:8, cf. Michlol, 196a. In Proverbs 1:22, Proverbs 1:32, the mute א is wanting.)
(in which, as in גּוים, the י plur. remains unwritten) is, in this mongrel form in which it is written (cf. Proverbs 7:7; Proverbs 8:5; Proverbs 9:6; Proverbs 14:18; Proverbs 27:12), made up of פּתים (Proverbs 1:22, Proverbs 1:32, once written plene, פּתיים, Proverbs 22:3) and פּתאים (Proverbs 7:7). These two forms with י and the transition of י into א are interchanged in the plur. of such nouns as פּתי, segolate form, "from פּתה (cogn. פּתח), to be open, properly the open-hearted, i.e., one whose heart stands open to every influence from another, the harmless, good-natured - a vox media among the Hebrews commonly (though not always, cf. e.g., Psalm 116:6) in malam partem: the foolish, silly, one who allows himself to be easily persuaded or led astray, like similar words in other languages - Lat. simplex, Gr. εὐήθης, Fr. nav; Arab. fatyn, always, however, in a good sense: a high and noble-minded man, not made as yet mistrustful and depressed by sad experiences, therefore juvenis ingenuus, vir animi generosi" (Fl.). The פּתאים, not of firm and constant mind, have need of ערמה; therefore the saying Proverbs 14:15, cf. Proverbs 8:5; Proverbs 19:25. The noun ערמה (a fem. segolate form like חכמה) means here calliditas in a good sense, while the corresponding Arab. 'aram (to be distinguished from the verb 'aram, ערם, to peel, to make bare, nudare) is used only in a bad sense, of malevolent, deceptive conduct. In the parallel member the word נער is used, generally (collectively) understood, of the immaturity which must first obtain intellectual and moral clearness and firmness; such an one is in need of peritia et sollertia, as Fleischer well renders it; for דּעת is experimental knowledge, and מזמּה (from זמם, according to its primary signification, to press together, comprimere; then, referred to mental concentration: to think) signifies in the sing., sensu bono, the capability of comprehending the right purposes, of seizing the right measures, of projecting the right plans.

Simple - Such as want wisdom. Young man - Who wants both experience and self - government.